The invention relates to a photovoltaic cell, a especially to thin film solar cells, each of which comprises a first electric contact preferably mounted on a carrier on which a first (rear) and a second (front) semiconductor layer of opposite conductivity type are arranged, a second (front side) electric contact connected to the second semiconductor layer, and a cover glass covering the cell, as well as to a method for the fabrication of such photovoltaic cells.
Photovoltaic cells, also known as solar cells, include a diodelike structure and can be composed of crystalline or amorphous substances. For example, reference is made to U.S. Pat. No. 4,064,521 or the German laid open application No. 27 32 933, in which thin film solar cells are described as being made of amorphous silicon or cadmium sulphide-cuprous sulphide. Thin film solar cells can consist of a substrate on the rear surface of which a metallic contact is applied, on which again at least one p-conducting or n-conducting thin layer on which an n-conducting or p-conducting second layer is applied. Then the uppermost layer is provided with an electrically contact which can be a metal grid or a transparent conductive coating. Thereafter the solar cells of the above construction can be encapsulated. This can be effected in such a manner that the conductors or semiconductors to be encapsulated by the substrate carrier as well as a cover glass, are hot-sealed and pressed (see for example German laid open Application No. 27 32 933).
In order to obtain a high degree of efficiency of a solar cell, among other requirements, it is necessary that the front surface electric contact facing the light source provides a high radiation transmission, thus keeping the shading losses to the solar cell as little as possible. Here it is known to produce a metallic grid mounted on a support of glass and to press it on to the solar cell by means of a hot-sealing adhesive, or to make the grid by vapor deposition of a metal at high vacuum through an appropriate mask. Fine line grids with a web spacing in the range of 1 mm are used for solar cells if the front surface semconductor layer has a sheet resistance in the range of K .OMEGA., as it is typical e.g. for the Cu.sub.2 S/CdS thin film solar cells. Further, when using a single contact component, the grids must have a minimum thickness in order to guarantee current conduction to the desired extent. Consequently in order to have low production and material costs, reduced radiation transmissibility must be tolerated.
Likewise, the contacts cannot be fired since manufacturing temperatures of &lt;400.degree. C. should be used. Therefore screen-printed firable compositions as they are required to be used with Si-solar cells cannot be considered. Even with a-Si-solar cells manufacturing temperatures of &lt;400.degree. C. must be maintained as otherwise the hydrogen will diffuse out.